The overall objective of this research is to improve our understanding of why adolescents start to use tobacco, alcohol, marijuana and other drugs, both over the counter (OTC) and illicit, and why some subsequently become problem users and abusers. The specific objectives and aims are as follows: 1) Collect two more waves of predictor and drug use data, at grade 11 and two years later, from a cohort of Southern California students on whom we already have up to three waves (grades 7-9 of self-report, parent, and school personnel data (N=4450). An additional 4000 students will be surveyed at grade 11; a sample of 1250 of these students who score the highest on a multivariate risk factor will also be followed two years later. The grade 11 will be collected in Southern California high schools by USC staff during year 01, and the final wave of data will be collected by mail or phone by the UIC Survey Research Lab in the spring of 1992 (year 03 of the grant). 2) Investigate the role of family variables and adolescent mental health in the onset of drug abuse. This work will be conducted mostly at USC. Specific aims regarding this objective include assessing the importance of latchkey status as a predictor of drug abuse in a multivariate context, investigating the relationship between latchkey status and other indicators of conventional social bonding, and examining the relationship between latchkey status and depression and their prediction of drug use. 3) Compare the goodness of fit of alternative explanatory theories of the onset of drug use and abuse. This work will be conducted at UIC. The specific aims within this objective include assessing the robustness and stability of junior high school student and parent predictors thorough post high school, comparing the goodness of fit of several alternative predictive theories of drug use and abuse, examining the relationships between micro- and macro-level predictors from various theories, and developing and testing the goodness of fit of an "optimum" integrated model. The proposed study is important because it: encompasses the high risk age range (12-18); includes data from parents (grade 7-9) and schools (grades 7-9 & 11); enables tests and contrasts of the most important of the existing theories; incorporates a wider range of variables than any other single study; includes data from an ethnically and socioeconomically diverse population; includes five waves of data; utilizes sophisticated analytical techniques to examine interactions and mediating relationships and to contrast models; has a large enough sample size to enable split-half testing and replication for all analyses; will have important implications for future prevention programs/research.